WO 2011/082815 A1 discloses a connecting rod, and the passage surface of the small end may define a plurality of dimples that extend axially along the bore surface and may further include profiled surfaces adjacent to the opposing edges of the small end passage. The profiled surfaces of the small end passage may be shaped to correspond to a bending shape of the piston pin during operation of the connecting rod. Said profiled surface meets in an axially central portion of said passage opening, each extending therefrom to a respective end of said passage and taper away from said axis moving in a direction from an axially central portion of said passage toward the respective opposing end of said passage opening edge. It is also disclosed a method of making a connecting rod comprising removing material from the passage surface to define a plurality of dimples and profiling opposing ends of said passage. In the above disclosed method, the plurality of dimples is manufactured prior to profiling said opposing ends of said passage opening.
The trumpet shape surface which is performed with a continuously crescent slope beginning from the center, increases an oil flow rate in comparison to a cylindrical surface, jeopardizing the lubrication performance. Moreover, as dimples functions as an oil reservoir, they become less effective at the profiled inner surface of the passage. As a result, the small end passage arrangement implies a process with higher cost and worse productivity.
In operation of the internal combustion engine the piston pin bends in a flexional movement within the small end passage. This deflection movement is induced by the periodic arising gas forces impacting the piston and the movement leads to a flexural bending of the piston pin.
This periodic bending induces an accommodation of the piston pin within the small end passage and the flexional movement begins in the middle of the small end passage and ends in both opposed edges. Due to this flexional movement from the middle to the edges the lubricating oil between the piston pin and the inner passage surface is squeezed out of the lubricating gap inducing a pumping effect or higher axial flow. Accordingly, the probability of contact between the piston and the connecting rod is increased due to lack of oil in the inner passage. Thus, it is desirable to reduce wear and to stabilize the oil film in the lubrication gap between the piston pin and the small end passage.
The dimples depth is defined at a predetermined distance which forms a common plane distanced from the bore opening axis and are produced prior to a profiling process associated. The dimples in the axially central portion of said bore opening are then deeper than dimples closer to opposing edges. Measuring of such dimples is complex and complicates securing that their shape, distribution and, ultimately, volumes are properly manufactured for best component performance.
WO 00/34696 A1 discloses a connecting rod defining a profiled small end passage which is shaped with an angled relief portion adjacent to each opening edge and a piston pin is inserted through the profiled small end passage and into portions of the piston for securing together the piston and the connecting rod. The profiled surface portions are shaped to provide a relief for the piston pin deflection and a piston pin can be inserted into said small end passage for securing together the piston and the connecting rod. The profiled relieves portions are shaped with a plurality of end-to-end frustoconical sections which define a curved surface. But the even, untreated inner passage surface may cause oil starvation providing dry contact between the small end passage and the piston pin.
US 2009/0145394 A1 discloses a connecting rod comprising a small end passage for a piston pin having a wavy profile extending between the opening edges. The wavy profile has at least one concave surface with a valley extending along a circumferential direction of the small end passage. The small end passage has a profile wherein the profile extends between opening edges of the connecting rod. The profile has at least one concave surface transitioning to convex surfaces on laterally opposite sides of the concave surface to provide, at least, a double wave form that facilitates a generally smooth load distribution and uniform flow of lubrication between the piston pin and the small end passage in use. The wavy geometry provided in the small end passage surface may cause an incompatible piston pin deformation, consequently, causing dry contact between the small end passage surface and the piston pin, most probably, in the convex regions of the wavy geometry. The wavy geometry may present another problem, namely the loss of hydrodynamic sustentation in the concave regions, these regions represent an excessive large clearance, as a consequence, the thickness of the oil film may increase, and, as another disadvantage, the oil pressure reduces and the oil load capacity decreases.